staging: dgnc: clean up header comments

TODO file has task: remove unnecessary comments. Driver uses some
custom comment format. Driver would be better if it used kernel doc
format.

Audit header file comments. Replace struct comments with kernel doc
format comments. Remove unnecessary comments.

Signed-off-by: Tobin C. Harding <me@tobin.cc>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>